It has well known that polyolefinic polymers are particularly sensitive to the ignition with flame; therefore they need a suitable protection especially for critical applications such as part of household electric appliances, construction materials, and interior decorative materials.
For these applications several studies to impart satisfactory fire resistance have been carried out.
For example, Japanese patents 53-92855, 54-29350, 54-77658, 56-26954, 57-87482, 60-110738 disclose a method for preparing flame retardant polypropylene resin compositions by using inorganic flame retardant additive like Magnesium hydroxide, aluminium hydroxide, hydrotalcite or the like.
All these additives, however, in order to be effective need to be added at a level higher than 50% (by weight) based on the weight of final composition with the result that the processability is bad and the mechanical properties are drastically deteriorated.
Also well known are flame retardant polymeric compositions based on halogenated (brominated or chlorinated) organic products such as those disclosed, for example, in Japanese patents 55-30739 and 8-302102. JP 8-302102 relates to a flame retardant polypropylene resin composition where the polymer is mixed with 8-15 wt % of an organohalogen compound (flame retardant A) and 1-3 wt % of an halogenated epoxy oligomer (flame retardant B) as well as with other additives, for example antimony trioxide. These additives have been recognised to be very effective for ranking both V2 and V0 flammability grade, according to the UL 94 standards, but they normally cause the corrosion of the equipment used for processing due to the emission of acids and will develop toxic fumes in case of fire. In addition, the corresponding polymeric articles show high blooming and are endued with poor weather resistance.
It has been also known that flame retarded polypropylene articles can be achieved with the use of an intumescent system based on two or three components comprising:                an acid component, generally phosphorus containing agent;        a foaming agent, generally a nitrogen containing product such as for example ammonium polyphosphate, melamine or the like;        a carbonific compound which is generally a sugar like product as for example mono-, di-, tri-pentaerythritol or tris (2-hydroxyethyl) isocyanurate (THEIC).        
U.S. Pat. No. 4,312,805 discloses self-extinguishing polymer compositions comprising an ammonium or amine phosphate and one or more nitrogen organic compound, while U.S. Pat. No. 4,253,972 discloses flame retardant polyolefin compositions comprising a pentate salt of an amino-s-triazine and a polyhydric alcohol. U.S. Pat. No. 4,198,493; U.S. Pat. No. 5,312,853; U.S. Pat. No. 4,727,102; U.S. Pat. No. 3,810,862; U.S. Pat. No. 4,198,493; WO 2004 063262 also disclose similar polymer compositions.
In all cases the additivation level of such flame retardant systems is normally in the range of from 25% to 35% wt on the weight of total compound and therefore the mechanical properties, the weather resistance and the aesthetic properties of corresponding polymer articles are not satisfactory.
WO 2005 019330, discloses a particular system suitable for ranking V2 in polypropylene homopolymer articles. The disclosed flame retardant polymeric composition has a low halogen content and comprises, as essential components:                a nitrogen containing compound such as a triazine or a mixture of triazines of general formula (I)        an halogen containing compound        a bismuth compound of formula BizAw         a compound selected from the group consisting of red phosphorus, a phosphorous compound and an organic compound        
In the described system, the halogen can be brought either by the nitrogen containing product, generally a melamine based material, or by the Bismuth salt or by both and the total halogen in the composition is quite low.
This interesting composition has been reported to be effective in unfilled homo-polypropylene only and even so it is not fully satisfactory because of the discoloration of polymer articles due to the negative interaction of components. In addition, it has to be noted that the bismuth compound, which is essential in the above cited prior art composition, might cause severe environmental problems (La medicina Biologica, October-December 2001—A.M:Pasciuto—XVI national meeting—Milan Feb. 6, 2001—Rome Sep. 6, 2001).